48-17-03\tSIKORSKY: Applies to Model S-51 Helicopters. \n\nCompliance required at each 800-hour inspection. \n\nIn order to preclude any malfunctioning of the main rotor gearbox due to the normal wear which may be expected to occur in the primary and secondary planet pinion shafts (Sikorsky P/N S-535524), these parts should be rotated 180 degrees or replaced by new parts after 800 hours of operation. If rotated, replacement by new parts should be made after an additional 800 hours. \n\n(Sikorsky Aircraft Service Information Circular No. 8 Revision "B" dated January 13, 1948, covers this same subject.) \n\n\n\nAD 48-17-03